He did not know how long it took, but later he looked back on this time of crying in the corner of the dark cave and thought of it as when he learned the most important rule of survival, which was that feeling sorry for yourself didn't work. It wasn't just that it was wrong to do, or that it was considered incorrect. It was more than that—it didn't work.
In Chapter 8 Brian articulates what he considers "the most important rule of survival." This moment represents a pivotal point in the novel's development and in the development of Brian's character. Although there are other pivotal moments, most notably Brian's suicide attempts and his subsequent emotional rebirth of sorts, this quote touches upon the first time that Brian adopts this thought process. This realization crops up countless times later in the book, and renews Brian's resolve to remain positive and motivated toward action.